Unit 1 Section 6.3 Transpiration

a plant needs to open its stomata to let in carbon dioxide so that it can produce glucose by photosynthesis

but this also lets water out,

as there is a higher water concentration inside the leaf than in the air outside so water moves out of the leaf down the water potential gradient when the stomata opens

so transpiration's really a side effect of the gas exchange needed for photosynthesis

Factors affecting transpiration rate

there are four main factors that affect transpiration rate:

1. LIGHT, the lighter it is the faster the transpiration rate. this is because the stomata open when it gets light

when its dark the stomata are usually closed, so there's little transpiration

2. TEMPERATURE, the higher the temperature the faster the transpiration rate. warmer water molecules have more energy so they evaporate from the cells inside the leaf faster

3. HUMIDIDTY, the lower the humidity, the faster the transpiration rate. if the air around the plant is dry, the water potential gradient between the leaf and the air is increased, which increases transpiration

4. WIND. the windier it is, the fasteer the transpiration rate. lots of air movement blows away water molecules from around the stomata. this increases the water potential gradient, which increases the rate of transpipiration

Estimating transpiration rate - potometers

a potometer is a special piece of apparatus used to estimate transpiration rates

it actually measures water uptake by a plant, but it's assumed that water uptake by the plant is directly related to water loss by the leaves.

you can use it to estimate how different factors affect the transpiration rate

Adaptations in xerophytic plants

xerophytes are plants like cacti, pine trees and prickly pears, which are adapted to live in dry climates. their adaptations prevent them losing too much water by transpiration

stomata are sunk in pits

a layer of 'hairs' on the epidermis

curved leaves

thick, waxy layer on the epidermis

spines instead of leaves

a reduced number of stomata

xerophytes are plants like cacti, pine trees and prickly pears, which are adapted to live in dry climates. their adaptations prevent them losing too much water by transpiration